Three-dimensional grading FeP nanosheet hydrogen evolution electro-catalytic material and preparation method and application thereof
Technical Field
The invention belongs to the field of electrocatalytic hydrogen evolution, and particularly relates to a three-dimensional graded FeP nanosheet hydrogen evolution electrocatalytic material as well as a preparation method and application thereof.
Background
With the continuous development of social economy, the energy consumption is increased in a leap-type manner. At present, the energy consumption of China still mainly utilizes non-renewable fossil fuels, and meanwhile, serious environmental pollution and greenhouse effect are brought. In order to cope with the gradual depletion of fossil fuels and the environmental problems caused by the depletion, an environment-friendly and renewable energy production mode is urgently sought.
As the cleanest energy carrier, hydrogen also has the characteristics of high energy density and reproducibility, and can be used as a novel fuel for replacing fossil fuels. The method for preparing hydrogen by electrolyzing water is considered to be an ideal sustainable energy production mode due to the advantages of simple equipment, relatively mature technology, high product purity, no pollution in the process and the like. A huge bottleneck exists in the water electrolysis industry, namely the electric energy consumption is large due to the over-high hydrogen evolution potential of the electrolysis electrode. Therefore, the development of a high-activity catalyst capable of effectively reducing the overpotential of hydrogen evolution of the cathode becomes a challenge and an urgent task for researchers in various countries.
At present, for the hydrogen evolution reaction process, the platinum group noble metal has the best electrocatalytic activity, but the platinum group noble metal has limited storage capacity on the earth, is very expensive, is easy to run off in the reaction process, and is not beneficial to realizing large-scale popularization. Therefore, the search for the elements which are efficient and rich in resources on the earth to replace platinum group metals to prepare cheap and durable non-platinum hydrogen evolution catalytic materials is vital to promote the development of the electrocatalytic hydrogen production technology.
Disclosure of Invention
The invention aims to provide a three-dimensional iron phosphide nanosheet material, and a preparation method and application thereof.
The invention provides a preparation method of a three-dimensional iron phosphide nanosheet material, which specifically comprises the following steps:
(1) soaking an iron material serving as an electrode into NaOH aqueous solution, and applying alternating voltage to the electrode to obtain aqueous solution containing reddish brown suspended matters;
(2) separating solid substances in the water solution containing the reddish brown suspended matters, washing and drying to obtain three-dimensional iron oxide nanosheets;
(3) three-dimensional iron oxide nanosheets and NaH2PO2·H2O crystal powder is respectively placed in two separated positions in a tube furnace, wherein NaH2PO2·H2And (3) taking O crystal powder as an upstream, and taking inert gas (such as argon) as carrier gas to perform heating and phosphorization reaction under the program setting of a tube furnace to obtain black three-dimensional iron phosphide nanosheet material.
Preferably, the ferrous material is iron wire.
Preferably, the concentration of the NaOH aqueous solution is 2-4 mol.L–1。
Preferably, the value of the alternating voltage is 7-10V, and the time for applying the alternating voltage is 1 h.
Preferably, the three-dimensional iron oxide nanosheets and NaH2PO2·H2The mass ratio of the O crystal powder is 1: 10.
Preferably, the program setting parameters of the tube furnace are as follows: at 2 ℃ min–1The temperature rising rate is increased from room temperature to 250-350 ℃, then the temperature is kept for 2-3 hours, and finally the natural cooling is carried out.
The three-dimensional iron phosphide nanosheet material provided by the invention is prepared by adopting the method. The three-dimensional iron phosphide nanosheet material can be used as an electrocatalyst for the electro-decomposition water-out hydrogen reaction.
Compared with the prior art, the invention has the following advantages:
(1) the three-dimensional nano-sheet iron oxide can be continuously generated at room temperature by treating the metal iron wire through the alternating voltage, the method has the advantages of simple required equipment, quick material formation, mild preparation conditions and low price of used materials;
(2) the alternating voltage method is only carried out in blank NaOH base solution, and a three-dimensional nanosheet structure can be generated without a precursor solution and a hard template, so that the method is very simple and green;
(3)NaH2PO2·H2o as phosphorus source, and generating reducing gas PH under low temperature heating3Reducing the three-dimensional nanosheet iron oxide into three-dimensional nanosheet iron phosphide, wherein the three-dimensional nanosheet structure is very stable;
(4) the three-dimensional nanosheet iron phosphide prepared by the method has huge surface area, tearing edges and abundant active sites on the nanosheets owned by folds and a large number of porous channels in hierarchical structures, which are very beneficial to surface reaction and mass transfer;
(5) the novel three-dimensional FeP nanosheet shows high-efficiency activity when being applied to electrolytic water hydrogen evolution reaction, and particularly has the activity of 10mA cm–2Very low overpotential (88 m)V), Small Tafel slope (47.7mV dec)–1) And satisfactory long-term stability.
Drawings
Fig. 1 is an XRD pattern of three-dimensional iron oxide nanoplates of step (1) of example 1.
Fig. 2 is an SEM image of three-dimensional iron oxide nanoplates of step (1) of example 1.
Fig. 3 is an XRD pattern of three-dimensional iron phosphide nanosheets of step (2) of example 1.
Fig. 4 is an SEM image of three-dimensional iron phosphide nanosheets of step (2) of example 1.
FIG. 5 shows that the three-dimensional iron phosphide nanosheets of example 2 are 0.5 mol.L as electrocatalysts–1H2SO4Linear sweep voltammetric polarization curves of (1).
Fig. 6 is a tafel slope curve fitted from a polarization curve using the three-dimensional iron phosphide nanosheets of example 2 as an electrocatalyst.
FIG. 7 shows three-dimensional iron phosphide nanosheets of example 2 as electrocatalysts at a constant temperature of 40mA cm–1Chronopotentiometric curve at current density.
Detailed Description
The surface appearance of the product prepared by the invention is measured by a Scanning Electron Microscope (SEM), the crystal structure of the material is measured by an X-ray diffractometer (XRD), and the catalytic activity of water electrolysis and hydrogen evolution is measured on a Shanghai Chenghua electrochemical workstation.
Example 1
(1) Preparing three-dimensional iron oxide nanosheets:
ultrasonically cleaning two iron wires (2cm long and 0.5mm in diameter) in acetone, absolute ethyl alcohol and deionized water for 20 min; immersing the dried iron wires into 4M NaOH aqueous solution in parallel for 0.5cm, and keeping the distance between the iron wires to be 1.5 cm; applying 8V alternating voltage to the two iron wires, and keeping the solution magnetically stirred for 60 min; collecting suspended matters in the electrolyte by centrifugation, and alternately cleaning the suspended matters with deionized water and absolute ethyl alcohol for 6 times, wherein the rotating speed of a centrifuge is 8000rpm, and the time of each time is 5 min; and (3) drying the cleaned product in an oven at 70 ℃ for 12h to obtain the three-dimensional iron oxide nanosheet.
In FIG. 1X-ray powder diffraction (XRD) analysis revealed that all diffraction peaks of the electrochemically stripped product from iron wire using an 8V AC voltage were ascribed to maghemite crystalline phase, tetragonal gamma-Fe2O3(JCPDS No. 25-1402), no other diffraction peaks were detected, indicating high purity of the resulting sample. Scanning Electron micrographs (see FIG. 2) show that these gamma-Fe2O3The product has a three-dimensional hierarchical continuous microstructure and is formed by cross-assembling a large number of two-dimensional smooth nanosheets (with the thickness of about 10nm) with uneven sizes and tearing-shaped wrinkle edges.
(2) Preparing three-dimensional iron phosphide nanosheets:
mixing the three-dimensional iron oxide nanosheet prepared in the step (1) with NaH2PO2·H2O crystal powder is put in two separated positions of a quartz tube furnace, NaH2PO2·H2O crystal powder is positioned at the upstream, and the mass ratio of the O crystal powder to the O crystal powder is 1: 10; subsequently, the atmosphere in the quartz tube was maintained at a high purity argon atmosphere, and the temperature raising program was set at 2 ℃ for min–1Raising the temperature from room temperature to 350 ℃, keeping the temperature for 120min, and continuously naturally cooling to room temperature under the argon atmosphere after heating; finally, a large number of black three-dimensional iron phosphide nanosheets were collected.
XRD analysis in FIG. 3 shows that upon low temperature phosphating, the maghemite phase Fe2O3The diffraction peak of (B) was completely disappeared and completely converted into orthorhombic FeP (JCPDS No. 89-2746). Meanwhile, the synthesized FeP also has a three-dimensional nanosheet structure (see FIG. 4). Phosphide FeP and its precursor Fe2O3The morphology of (a) is slightly different in that the smooth nanosheets expand and thicken, and many compact tiny nodules appear on the surface.
Example 2
And (3) testing the performance of the three-dimensional iron phosphide nanosheet as the catalyst for the electrolytic water hydrogen evolution reaction:
(1) preparing an electrocatalyst working electrode:
adding 5mg of three-dimensional iron phosphide nanosheet powder and 50 mul of 5 wt% nafion solution into 950 mul of ethanol, and carrying out ultrasonic treatment for 15 min; adding 1.5mg of carbon black powder into the mixed solution, and continuing performing ultrasonic treatment for 30min to form uniform catalyst ink; 5 mul of catalyst ink is transferred and coated on the surface of a glassy carbon electrode (with the diameter of 3mm), and the surface is naturally dried to be tested.
(2) Electrochemical performance study:
the electrochemical properties of the prepared samples were tested on the CHI 660E electrochemical workstation (chenhua instrument, shanghai, china). A traditional three-electrode system, namely a Pt sheet electrode as a counter electrode, a Saturated Calomel Electrode (SCE) as a reference electrode and a catalyst modified glassy carbon electrode as a working electrode is used. 0.5 mol. L–1H2SO4The aqueous solution serves as a supporting electrolyte. Unless otherwise indicated, all potentials in the tests were converted to Reversible Hydrogen Electrode (RHE) potentials according to the nernst equation.
FIG. 5 shows that the three-dimensional iron phosphide nanosheet is 0.5 mol.L as an electrocatalyst–1H2SO4Linear sweep voltammetric polarization curves of (1). The figure shows that the three-dimensional iron phosphide nanosheet has good electrocatalytic activity, and the electrocatalytic decomposition water reaction initial overpotential (defined as the obtained current density of-1 mA-cm)–2Overpotential of) is only 39mV, resulting in-10 mA cm–2The reference current density (equivalent to the current density produced by a 12.3% efficient solar water splitting plant) only needs 88 mV.
FIG. 6 is a Tafel slope curve of three-dimensional iron phosphide nanosheets as an electrocatalyst. The figure shows that the three-dimensional iron phosphide nanosheet has a lower Tafel slope (only 47.7mV dec)–1) The slope is-120 mV · dec–1The interval shows that the mechanism of the catalytic hydrogen evolution reaction is a Volmer-Heyrovsky catalytic mechanism, namely the mechanism consists of a rapid electrochemical reaction step and a slow electrochemical desorption step, and the electrochemical desorption step is a rate control step.
FIG. 7 shows that three-dimensional iron phosphide nanosheets are used as electrocatalysts at 40 mA-cm–1Chronopotentiometric curve at current density. At constant current density (40mA cm)–1) During the continuous test for 20 hours, the overpotential only needs to be applied not more than 145mV, reflecting that the material has high electrocatalytic activity and stability in an acid electrolyte.